multi-tenant & multi-server install - appliance vs standard method

We are in the process of planning a Zimbra 8 multi-tenant deployment. I've been reading the admin guide and it seems pretty straight forward, we will most likely separate the mailbox role from the mta and ldap, however I have a few questions and was wondering if anyone here had any recommendations based on best practices or experience.

This is a new install, so there's nothing we are upgrading from, so I have no limitations as far as the config goes.

I guess the first question is appliance vs standard install on Ubuntu, etc - we've been using the appliance for standalone servers with a lot of success, but I was wondering if there are any advantages or disadvantages with a multi-tenant install that will need to scale over time?

Second question is role separation - I'd like mailboxes on their own server, but as far as ldap and mta, any real reason to isolate those? In the appliance it seems to force you to use a separate appliance for each role, but in the standard install I believe I can have more granular option and merge a couple (correct me if I'm wrong on this).

Initially we'll have a single mailbox server but I can imagine this scaling out quickly and having multiple within the next 12 months if that has any bearing on your recommendations on role separation for ldap and mta.

We haven't deployed anything yet, still in the design phases so I'm really open to anything on this.

We am currently working on something very similar to your purposed setup. We have decided to separate everything as follows:

1) MTA, Proxy, Bind, Memcache
2) LDAP - Master
3) Mailstore

The reasoning behind our separation is for troubleshooting as we grow. Eventually we will move proxy and memcache to a separate server and bind to a separate server. We have also decided to go with standard install on ubuntu 12.04 as opposed to the appliance. No particular reason other than we have used the standard install before with no issues and feel comfortable with it.

Thanks for the response - we've opted to go with Ubuntu as well vs the appliance, mainly due to famliarity.

After talkign to some engineers at Zimbra we'll probably end up with a dedicated proxy, but on the rest we're going to scale out horizontally for now. This was based on initial mailbox counts and projected growth.

We ended up following the step by step below and so far it seems to be working. We are able to send mail. Now we just need to figure out where to point what ports. The only difference we made is we went with a dedicated DNS server (bind9).